I mean the most common definition is whether or not they could reproduce with each other. I have seen some novel of the same genre defining them as different race and be able to mate, so I see it's accurate.

There can also be geographically separated species that have viable, fertile offspring when they reproduce together, but they're still considered separate species because the two populations aren't naturally reproducing with each other.

I asked my microbiology teacher for a definition of species and he could not give me one.

Any definition based on reproduction immediately faces problems because many species reproduce solely asexually. I came up with the idea that any two organisms whose DNA differs by <X, where X is a constant generally accepted by the scientific community, are part of the same species. The problem I realized is that this means that there is no Transitive Property of Species (a term I just coined), which is really weird in its implications.

Yeah, we've answered your surface question ("yes, no, or maybe, depending on which definition of 'species' you're using, because there are a lot of them"). Since you're still asking, that means there's a question behind your question that you're really trying to answer. Ask that one directly.

(I suspect your actual question is "in my fantasy world, do scientists call them the same species or different?", which we can't answer - you have to decide that.)

Angua wrote:Consider the question - are Vulcans the same species as human?

Clearly not. I define species based on the colour of their blood.

In most fiction, anything that resembles a human can reproduce with humans. Demons, or even tentacle monsters, are clearly not the same species as the humans who bear their children. Most people know it's biologically wrong, but it's typical enough in many stories that any attempt to shine a light on it in your fiction is likely to get more sarcastic "okay, thank you for breaking my suspension of disbelief" reactions than "whoa, that's deep" reactions.

"The textbook examples of ring species, including the circumpolar herring gull complex, the greenish warbler of Asia, and the Ensatina salamanders of America, have all been challenged, so ring species are at best rare."

.

Are there unambiguous current ring species (in addition to any which may have existed before, but don't anymore) ?

I found my old forum signature to be awkward, so I'm changing it to this until I pick a better one.

jewish_scientist wrote:I asked my microbiology teacher for a definition of species and he could not give me one.

Any definition based on reproduction immediately faces problems because many species reproduce solely asexually. I came up with the idea that any two organisms whose DNA differs by <X, where X is a constant generally accepted by the scientific community, are part of the same species. The problem I realized is that this means that there is no Transitive Property of Species (a term I just coined), which is really weird in its implications.

No usable definition of species is going to be transitive, though. For every other thing that has ever lived on Earth, there's a chain of organisms connecting you to that thing, and each organism in the chain is considered to be the same species as the ones on either side of it.

Unless stated otherwise, I do not care whether a statement, by itself, constitutes a persuasive political argument. I care whether it's true.---If this post has math that doesn't work for you, use TeX the World for Firefox or Chrome

At best, one can suggest the temporal boundary of death of the Most Recent Common Ancestor (or perhaps Most Recent Breedable Cousins would be better1) as the emergent points of the "watersheds" between the streams of species that ultimately flow back and merge with the First Ancestor/whatever.

But good luck actually empirically testing and recording that to sufficient depth and width across the whole tree of life...

1 But accept the possibility that the first unbreedable nth cousins may yet beget n+kth cousins that have random genetic drift or allelle re-convergence sufficient to believably breed again, given both opportunity and inclination...

Linguistics suffers from a similar issue (defining when two dialects become different languages, and indeed, what make two things different dialects in the first place) and, as a result, has often started using "variety" as a way of recovering a similar sense without establishing a level in a hierarchy. I think it's roughly equivalent to "taxon" in biology.

E.g. Cockney is a variety of English which is a variety of Anglo-Frisian which is a variety of Germanic which is a variety of Indo-European

Similarly in biology one could just start using "taxon" at all levels

E.g. humans are a taxon of primates which are a taxon of mammals which are a taxon of animals etc

This recovers transitivity and resolves the question of is the thing a subspecies or separate species but it still has issues with ring species (or similar things though) because with those the issue is that these things are fundamentally not discrete but can be a continuum (which is where the issues of ring species and dialect continua arise).

eSOANEM wrote:Linguistics suffers from a similar issue (defining when two dialects become different languages, and indeed, what make two things different dialects in the first place) and, as a result, has often started using "variety" as a way of recovering a similar sense without establishing a level in a hierarchy. I think it's roughly equivalent to "taxon" in biology.

But we do have a perfectly good distinction between a language and a dialect already - "a language is a dialect with an army."

Science, and the methods by which we reach a scientific consensus, are not so pure, extra especially when it comes to questions of demarcation. If you are writing a fantasy setting, there will surely be different groups that stand to benefit from the question being one way or another. Those supporting elf-suffrage may say they're all just samesies, the beastmen separatists may disagree. A scientist can be found who thinks anything you like, and they can be promoted and their thoughts propagated.

LE4dGOLEM: What's a Doug?Noc: A larval Doogly. They grow the tail and stinger upon reaching adulthood.